Is this related to using K Ferri as an overall reducer, local dabbed on reducer, or when combined with with K Br as a re-halogenating bleach?
There are also esoteric uses likel bleaching back a latent image prior to development in lieu of n-x development approaches when the contrast range in a scen is very large.
Then there are discussions as it relates to cyanotype.
I have different articles clipped from various publications over the years on all of these issues, but alas not the Barnbaum PT article you seek.